It has long been a goal in the art to find a combination power source (i.e., drive) and transmission device that can deliver the peak output of the power source over a large range of the rotational speed (rpm) output of the transmission device. Further, it is preferable that this peak power be output from the transmission device, or from the drive device incorporating the transmission device, at continuously variable speeds of rotation over a large range of the speed of rotation of the output. A transmission device making possible such properties is known in the art as an infinite speed transmission device. The term “drive and transmission device” or “combination motor and drive device” is employed in the present disclosure to describe the case of the device including the drive means (i.e., power source means) as well as the transmission means. The term “motor and transmission device” or “combination motor and transmission device” is employed for the case of the drive means including an electric motor means, as the drive means (i.e., power source).
Known transmission devices typically involve a single rotational mechanical input and a single rotational mechanical output. Such known transmission devices, whether manual or automatic, may typically employ a set of gears. In these transmissions, the ratio of the speed of rotation of the input to the speed of rotation of the output is one of a set of fixed values corresponding to the set of gears. These typically involve a large number of parts, undesirable weight for many applications particularly in vehicle propulsion, and high losses due to multiple transfers of the power between the many components within the transmission device, or within the drive device incorporating the transmission device.
Differential units and planetary gear units are known in the art as transmission devices. Known planetary gear types of transmission devices involve an inner sun gear, an outer ring gear and a set of planetary gears held by a hub to rotate between the sun gear and the ring gear. When the sun gear rotates with respect to the ring gear, the planetary gears rotate between them, and the hub rotates accordingly, coaxially with the sun and ring gears. In a typical prior art use of the planetary gear unit, the hub is fixed, and either the sun gear or the ring gear is driven as the rotational mechanical input, the other providing the rotational mechanical output. Alternatively, either the sun gear or the ring gear can be fixed, the other is either the rotational mechanical input or output, and the hub provides the other of the rotational mechanical input or output.
One advance in infinite speed drive and transmission devices is described in U.S. Pat. No. 5,067,932 to Edwards, entitled Dual-Input Infinite Speed Integral Motor and Transmission Device. This patent, which is hereby incorporated by reference in its entirety, provides an infinite speed combination motor and transmission device having two inputs, with at least one of the inputs being an integral combination of an electric motor element and a transmission unit element. In one embodiment, two integral electric motors provide input to two of the three gear units in a planetary gear system (the ring gear and planetary gear hub, in particular) with the third gear providing an infinitely variable mechanical output (the sun gear in this case).
An important advantage of the Edwards patent is that the braking of a vehicle can be performed by using the electric motors as generators, namely by regenerative braking. In the case of a battery powered car, the kinetic energy of the vehicle can be converted back into useable electricity charged back into the battery, and hence available for subsequently propelling the car. Thus, a small lightweight hydraulic brake, such as on each wheel, suffices as backup and emergency brakes for the vehicle. The infinite-speed characteristic of the combination motor and transmission device is particularly useful for this purpose, namely in being able to adjust the device for maximum regeneration. In generic terms this involves converting the mechanical output into an input, and the two electric motor inputs into two outputs, or one output and one input.
A still further advance is described in U.S. Pat. No. 5,851,162 to Tether. This patent, which is hereby incorporated herein by reference, relates generally to a system for propelling various types of vehicles that incorporate or require multiple output propulsion devices. In particular, the Tether patent relates to a motor transmission system for an electric vehicle that uses a plurality of combined electric motor and transmission devices with a continuously variable speed output and a stored energy supply for powering the device. This device sets out to reduce the cost and complexity of electric motor transmission devices while at the same time reducing the complexity of its control.
In one specific example, the Tether patent provides a multiple input, dual output differential motor transmission device that incorporates a sun gear device having first and second sun gears fixedly connected to each other whereby the first and second sun gears rotate together along a common axis of rotation; first and second ring gear devices having first and second ring gears, respectively; and first and second sets of planetary gears. The first set is inter-engaged between the first sun and ring gears, while the second set is inter-engaged between the second sun and ring gears. The first sun and ring gears are concentrically and independently rotatable relative to each other with the first set of planetary gears inter-engaged therebetween. The second sun and ring gears are concentrically and independently rotatable relative to each other with the second set of planetary gears inter-engaged therebetween. Rotation of at least one of the first and second sun gears together, the first ring gear and the second ring gear generates at least one of rotational and revolving movement of a corresponding one of the first and second sets of planetary gears.
While the Tether patent adds significantly to the art, motor-transmission device configurations that continue to reduce the number of moving parts and allow the device to be used in ever smaller spaces will allow the adoption of such devices into more and more applications.